Flashing is used throughout building construction to weatherproof roofing and other external building cladding membranes around discontinuities such as roof edges, juncture points with walls, around roof penetrations, such as pipes, supports for roof mounted equipment, and stacks which project through the roof.
Conventional flashing is constructed of thin sheet metal which is cut and assembled on site, or may be prefabricated for quick assembly on site. Typically, sheet metal flashing is assembled from components on the building site by spot welding, with snap lock joints, or with self-tapping screws. To complete the required weather seal, the flashing is soldered along exposed joints or sealed with caulking. A cap or counterflashing is assembled to around seal the penetrations at the top of the flashing.
The safe and proper installation of roofing, and other building weatherproofing membranes such as sheet metal external cladding, require favourable weather conditions. The high elevation and exposure to wind make safety a major concern. Wet weather makes surfaces slippery rendering such operations unsafe, introduces undesirable moisture into insulation etc., and impedes the proper bonding of adhesives and bitumen. Cold weather, snow or ice also make operations unsafe, and impractical in many cases. Strong winds lift roofing materials during installation and create safety hazards for workers. In general it is preferable to conduct operations in daylight. Accordingly, there are a limited number of months and limited days of those months where roofing or cladding operations may be carried out economically and safely, especially in northern climates.
As a consequence, the minimization of on site labour is a highly significant factor to achieve rapid installation during favourable weather conditions. Conventional methods of reducing on site labour include the prefabrication of standardized roofing and flashing components. The prefabricated flashing components can then be rapidly assembled on site, saving time and money.
Examples of such prefabricated roof flashing are described in the following prior art. U.S. Pat. No. 4,937,991 to Orth describes a stainless steel sheet metal split flashing that is prefabricated to fit around a pipe extending through a roof. The opposing edges of the prefabricated split flashing are quickly snap locked and lap spliced together on site. However, to complete the weatherproof sealing of the flashing it is necessary to solder the seams together in a conventional manner.
U.S. Pat. No. 280,085 to Sage describes a prefabricated split sheet metal flashing joined together along joints with C-shaped sliding sheet metal clips coacting with bent metal ridges on joint edges of the prefabricated flashing components. Again the only revealed means to seal such flashing is conventional soldering of the joints after assembly, or caulking. U.S. Pat. No. 1,072,199 to Wood and U.S. Pat. No. 3,368,369 to Miller describe similar prefabricated metal flashing assemblies with various interlocking joint features, but utilizing the conventional means of weatherproofing the joints.
A significant disadvantage of using conventional prefabricated flashing is that despite the elimination of on site cutting and fitting, the flashing is still sealed in a labour intensive manner, namely with soldering or caulking. Therefore, when favourable weather allows installation, the amount of labour required to complete the sealing necessary for a weatherproof installation of the flashing remains significant. As well, the level of skill remains high since skilled workers are relied upon to produce a critically important weatherproof seal in the flashing. If the soldering or caulking work is not of consistently high quality, leakage will occur resulting in costly repairs and reworking.
An additional disadvantage in use of conventional metal roof flashing is experienced during roofing repairs or complete reroofing. Conventional metal flashing is typically discarded during reroofing operations since the thin sheet metal is cut and distorted to remove it from the old roof. Although reuse and recycling are becoming more important, the best that can be done with conventional metal flashing after removal is to separate the different metals, such as copper, aluminium, galvanized or stainless steel, and sell them as scrap metal. If the volume of metal is not significant, even such recycling can be uneconomical and impractical. As a result, the old metal flashing is often simply removed and discarded during reroofing. New metal flashing is then installed with the new roof.
A typical flat roof for industrial or commercial buildings lasts about 10 to 15 years before leakage occurs and repairs increase to the point where complete replacement is the most economical solution. In contrast, most building components, and particularly sheet metal components, can have a much longer economical life of fifty or one hundred years if properly maintained. Roofing is also replaced in order to better insulate older buildings by installing rigid insulation on roof decks.
In the life span of a typical industrial or commercial building then, the periodic replacement of a roof, and in particular the removal and replacement of metal flashing can be a significant expense in building maintenance.
Prior to the present invention, reroofing has involved disposal of relatively expensive metal flashing and complete replacement. Since corrosion resistant metal is used such as cooper, aluminium, galvanized or stainless steel, the old metal flashing used is often in good serviceable condition when the bituminous roofing material has deteriorated. The soldering of conventional thin sheet metal flashing and coating with bitumen etc. during roofing makes it necessary to sacrifice metal flashing of good quality in order to replace the rest of the roof which has deteriorated. The waste of uncorroded material and cost of replacing flashing is substantial.
It will be understood that although this description of prior art and the invention is focused on use in built up bitumen roofing construction, the same considerations and scope of the invention relate to any waterproof membrane such as sheet metal wall cladding, or aluminium siding which also use sheet metal flashing assemblies. It will also be understood that the prior art and invention are not restricted to sheet metal flashing but also include spun or extruded aluminium, or molded plastic flashing.
It is desirable therefore to produce a prefabricated flashing which is quickly assembled and facilitates rapid completion of the weatherproof seal, while providing high reliability.
It is also desirable to produce metal flashing that can be reused in order to reduce costs during reroofing operations and to reduce the waste involved.